The present invention is directed to an apparatus and method for eliminating short pulses in a Doppler radar, whether or not the pulses are pulse compressed.
In radars intended for the detection and location of ground mobile vehicles, it is necessary to operate in short and spaced sound strokes in order to reduce the probability of destruction by an anti-radiation missile and to reduce its susceptibility to counter-measures. The echoes of a target vehicle must be detected and localized very rapidly. This requires the provision of automatic means to avoid a radar operator being subjected to many false alarms coming from the residue of clutter and from active or passive interference signals. This indispensable automatic control of the amount of false alarms should take into account the particular nature of the targets and the characteristics of various stray current signals that may exist.
A false alarm is caused by the presence, in a resolution cell of the radar, of a stray current signal exceeding the previously established threshold of detection. This stray current signal can arise, either from a stray current echo from an exterior source, or from a range sidelobe due to pulse compression and resulting from the presence of a useful signal of a significant level in a resolution cell near the resolution cell in which the stray current signal manifests itself.
The presence of a short pulse, i.e., present only in a given range gate, involves the appearance in the treatment (signal processing) chain of the signal, Doppler filter and integrator, of a transient state corresponding to a pulse response of the chain. For an amplitude of stray current signal more than twenty decibels above the normal noise of the radar, this transient state is detected and causes a false alarm. In the presence of strong fixed echoes, or normal noise, this false alarm causes a degradation of the radar's elimination capability, which reduces its operational usefulness.